WESTMINSTER ABBEY is to have a new tower and its museum and gallery are to be expanded, in the most significant changes to the building since the 18th century.

The Dean and Chapter announced on Thursday of last week that they had been given planning permission by Westminster Council to construct the tower at the eastern end of the Abbey, to contain a lift and stairs up to the eastern triforium.

An existing public gallery there, which is rarely visited because it is difficult to obtain access to it, will be renovated and expanded, and renamed the Queen's Diamond Jubilee Galleries.

The new tower has been designed by the Abbey's architect and Surveyor of the Fabric, Ptolemy Dean, and will be built in a similar Gothic style to the rest of the Abbey, nestling unobtrusively into the corner between the Lady chapel and the Chapter House.

The project will cost almost £19 million, the Abbey said. The money will come from fund-raising, and almost £11 million has already been raised. Ambitious plans to add a £10-million corona to the roof were shelved in 2013.

The Dean of Westminster, the Very Revd John Hall, described the plans as the "most exciting development of the Abbey building for over 250 years. This planning approval will enable us to approach with confidence the final stages of the necessary fundraising, and drive us towards the timely completion and opening of the Queen's Diamond Jubilee Galleries."

The Galleries will display many of the Abbey's historic treasures, including the velvet cope worn by a Dean of Westminster at the coronation of Charles II in 1661, and the Liber Regalis, a 14th-century illuminated manuscript that sets out the procedure for coronations.

Westminster Abbey is a UNESCO World Heritage Site and welcomes about two million visitors each year. The project is expected to be complete by 2018.